Deutschen Zahnartzlichen Zeituno, 41, pages 525-526 (1986) describes the production of a metal sleeve crown from solid material by means of spark erosion. Here an individual wax body modeled on a casting or in the mouth of the patient is plated about 1 mm thick with copper above and below a plane defined by the crown equator. This galvanically shaped element is separated at the equator so as to produce two shaping electrodes by means of which a tooth replacement part can be produced from a metal blank. Both shaping electrodes sink corresponding to the erosion removal into the metal body and thus form the tooth replacement part, for instance a top crown. The advantage of this method is that standard noble metals and nonnoble metal alloys can be machined, in particular those which cannot or can only be cast with great difficulty. During the tooth replacement part production mistakes which are caused by errors in the dimensions or interfitting of the dies during casting are largely eliminated. The disadvantage of this method is however that the natural teeth or the correspondingly shaped wax model has no clearly defined equator plane, since the tooth equator extends both vertically or horizontally in a nonstraight manner. If one assumes a central section plane it is necessary to take undercuts into account that cannot be produced by spark erosion.
Thus U.S. Pat. No. 4,904,348 describes how to mount the positive wax models on a common carrier such that casting molds can be made and shaped. The individual tooth replacement parts are aligned in a common equatorial plane that is set at the widest part of their section such that this equatorial plane is the split plane for the subsequent eroding electrodes. In a further step of the method the spaces between the individual replacement parts up to the equatorial plane are filled in order at first to produce the upper electrode, so that during filling of the space between the individual teeth of the replacement wax model one or more orienting pins is set perpendicular to the equatorial plane. After hardening of the cast mass, for instance a silicone mixture, the surfaces are cleared of impurities and the clean model is plated with a thin layer of silver which serves as a conductive layer for the subsequent eroding electrodes After galvanic copper plating these are stabilized by reinforcement and can be used as eroding electrodes. To produce second electrodes the first model is inverted by 180.degree. and is set in a form whose base is filled with a hardenable support mass. After hardening of the support mass another silver layer is applied to the surfaces and plated over with copper. The disadvantage of this is that an arbitrary equatorial plane as described above must be set, and in addition the individual wax models are aligned in a casting mold that is positioned by means of spacers which must be separately built. In order to spare time during the spark-erosion as desired it is not possible that in a unit of time a predetermined number of electrode sparks, according to the applied voltage, can be produced.
In general the above-described methods further have the disadvantage that the wax model is unprotected not only during pulling off of the plaster model but also during preparation or production of the copper electrode and is in danger of being deformed. The exact alignment of the wax model or of the copper electrodes relative to each other is also not described in the art.